Add classes to ERD elements

docs/entityRelationshipDiagram.md

@@ -5,17 +5,19 @@
 Note that practitioners of ER modelling almost always refer to *entity types* simply as *entities*.  For example the CUSTOMER entity type would be referred to simply as the CUSTOMER entity.  This is so common it would be inadvisable to do anything else, but technically an entity is an abstract *instance* of an entity type, and this is what an ER diagram shows - abstract instances, and the relationships between them.  This is why entities are always named using singular nouns.
 
 Mermaid can render ER diagrams
-```
+
+```mermaid
 erDiagram
     CUSTOMER ||--o{ ORDER : places
     ORDER ||--|{ LINE-ITEM : contains
-    CUSTOMER }|..|{ DELIVERY-ADDRESS : uses 
+    CUSTOMER }|..|{ DELIVERY-ADDRESS : uses
 ```
+
 ```mermaid
 erDiagram
     CUSTOMER ||--o{ ORDER : places
     ORDER ||--|{ LINE-ITEM : contains
-    CUSTOMER }|..|{ DELIVERY-ADDRESS : uses 
+    CUSTOMER }|..|{ DELIVERY-ADDRESS : uses
 ```
 
 Entity names are often capitalised, although there is no accepted standard on this, and it is not required in Mermaid.
@@ -31,9 +33,11 @@ ER diagrams are a new feature in Mermaid and are **experimental**.  There are li
 ### Entities and Relationships
 
 Mermaid syntax for ER diagrams is compatible with PlantUML, with an extension to label the relationship.  Each statement consists of the following parts, all of which are mandatory:
-```
+
+```mermaid
     <first-entity> <relationship> <second-entity> : <relationship-label>
 ```
+
 Where:
 
 - `first-entity` is the name of an entity.  Names must begin with an alphabetic character and may also contain digits and hyphens
@@ -43,17 +47,17 @@ Where:
 
 For example:
 
-```
+```mermaid
     PROPERTY ||--|{ ROOM : contains
 ```
 
 This statement can be read as *a property contains one or more rooms, and a room is part of one and only one property*. You can see that the label here is from the first entity's perspective: a property contains a room, but a room does not contain a property.  When considered from the perspective of the second entity, the equivalent label is usually very easy to infer. (Some ER diagrams label relationships from both perspectives, but this is not supported here, and is usually superfluous).
 
 ### Relationship Syntax
 
-The `relationship` part of each statement can be broken down into three sub-components: 
+The `relationship` part of each statement can be broken down into three sub-components:
 
-- the cardinality of the first entity with respect to the second, 
+- the cardinality of the first entity with respect to the second,
 - whether the relationship confers identity on a 'child' entity
 - the cardinality of the second entity with respect to the first
 
@@ -68,13 +72,37 @@ Cardinality is a property that describes how many elements of another entity can
 
 ### Identification
 
-Relationships may be classified as either *identifying* or *non-identifying* and these are rendered with either solid or dashed lines respectively. This is relevant when one of the entities in question can not have independent existence without the other.  For example a firm that insures people to drive cars might need to store data on `NAMED-DRIVER`s. In modelling this we might start out by observing that a `CAR` can be driven by many `PERSON` instances, and a `PERSON` can drive many `CAR`s - both entities can exist without the other, so this is a non-identifying relationship that we might specify in Mermaid as: `PERSON }|..|{ CAR : "driver"`.  Note the two dots in the middle of the relationship that will result in a dashed line being drawn between the two entities.  But when this many-to-many relationship is resolved into two one-to-many relationships, we observe that a `NAMED-DRIVER` cannot exist without both a `PERSON` and a `CAR` - the relationships become identifying and would be specified using hyphens, which translate to a solid line: 
+Relationships may be classified as either *identifying* or *non-identifying* and these are rendered with either solid or dashed lines respectively. This is relevant when one of the entities in question can not have independent existence without the other.  For example a firm that insures people to drive cars might need to store data on `NAMED-DRIVER`s. In modelling this we might start out by observing that a `CAR` can be driven by many `PERSON` instances, and a `PERSON` can drive many `CAR`s - both entities can exist without the other, so this is a non-identifying relationship that we might specify in Mermaid as: `PERSON }|..|{ CAR : "driver"`.  Note the two dots in the middle of the relationship that will result in a dashed line being drawn between the two entities.  But when this many-to-many relationship is resolved into two one-to-many relationships, we observe that a `NAMED-DRIVER` cannot exist without both a `PERSON` and a `CAR` - the relationships become identifying and would be specified using hyphens, which translate to a solid line:
 
-```
+```mermaid
     CAR ||--o{ NAMED-DRIVER : allows
     PERSON ||--o{ NAMED-DRIVER : is
 ```
+
 ### Other Things
 
 - If you want the relationship label to be more than one word, you must use double quotes around the phrase
 - If you don't want a label at all on a relationship, you must use an empty double-quoted string
+
+## Styling
+
+### Config options
+
+For simple color customization:
+
+| Name     | Used as                                                 |
+| :------- | :------------------------------------------------------ |
+| `fill`   | Background color of an entity                           |
+| `stroke` | Border color of an entity, line color of a relationship |
+
+### Classes used
+
+The following CSS class selectors are available for richer styling:
+
+| Selector                   | Description                                           |
+| :------------------------- | :---------------------------------------------------- |
+| `.er.entityBox`            | The box representing an entity                        |
+| `.er.entityLabel`          | The label for an entity                               |
+| `.er.relationshipLabel`    | The label for a relationship                          |
+| `.er.relationshipLabelBox` | The box surrounding a relationship label              |
+| `.er.relationshipLine`     | The line representing a relationship between entities |

src/diagrams/er/erRenderer.js

@@ -43,6 +43,7 @@ const drawEntities = function(svgNode, entities, graph) {
     const textId = 'entity-' + id;
     const textNode = groupNode
       .append('text')
+      .attr('class', 'er entityLabel')
       .attr('id', textId)
       .attr('x', 0)
       .attr('y', 0)
@@ -65,6 +66,7 @@ const drawEntities = function(svgNode, entities, graph) {
     // Draw the rectangle - insert it before the text so that the text is not obscured
     const rectNode = groupNode
       .insert('rect', '#' + textId)
+      .attr('class', 'er entityBox')
       .attr('fill', conf.fill)
       .attr('fill-opacity', '100%')
       .attr('stroke', conf.stroke)
@@ -148,6 +150,7 @@ const drawRelationshipFromLayout = function(svg, rel, g, insert) {
   // Insert the line at the right place
   const svgPath = svg
     .insert('path', '#' + insert)
+    .attr('class', 'er relationshipLine')
     .attr('d', lineFunction(edge.points))
     .attr('stroke', conf.stroke)
     .attr('fill', 'none');
@@ -224,6 +227,7 @@ const drawRelationshipFromLayout = function(svg, rel, g, insert) {
 
   const labelNode = svg
     .append('text')
+    .attr('class', 'er relationshipLabel')
     .attr('id', labelId)
     .attr('x', labelPoint.x)
     .attr('y', labelPoint.y)
@@ -241,6 +245,7 @@ const drawRelationshipFromLayout = function(svg, rel, g, insert) {
   // Insert the opaque rectangle before the text label
   svg
     .insert('rect', '#' + labelId)
+    .attr('class', 'er relationshipLabelBox')
     .attr('x', labelPoint.x - labelBBox.width / 2)
     .attr('y', labelPoint.y - labelBBox.height / 2)
     .attr('width', labelBBox.width)